package mao.exaimnation.netease;

/**
 * @author Totoro
 * @date 2020/8/8
 * @explain:
 */
// 将数字尽可能多地拆成素数，贪心，都拆成2，将1丢弃（可以和最后一个一结合成3）
import java.util.Scanner;
public class Main1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long res = 0;
        while (scanner.hasNext()){
            res = 0;
            int n = scanner.nextInt();
            for (int i = 0; i < n; i++) {
                res += scanner.nextInt()>>1;
            }
            System.out.println(res);
        }
    }
}